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Why does MMWD ask customers to conserve water even when the reservoirs are at normal levels or above?

Even when full, our reservoirs hold only about a two-year supply of water. A dry year or two can have a big impact on our supply. For example, in January 2013 our reservoirs were completely full; one year later they were nearly half empty due to the drought. Since we don't know from one year to the next how much rainfall we will receive, it's always important to use water wisely to help preserve as much water in our reservoirs as possible. Thank you for doing your part!

Even when full, our reservoirs hold only about a two-year supply of water. A dry year or two can have a big impact on our supply. For example, in January 2013 our reservoirs were completely full; one year later they were nearly half empty due to the drought. Since we don't know from one year to the next how much rainfall we will receive, it's always important to use water wisely to help preserve as much water in our reservoirs as possible. Thank you for doing your part!

The capacity of each reservoir is set by the elevation of the dam, which in turn is set by the water rights accorded to MMWD by the State of California (see next question). Once a reservoir is full, any additional water will flow naturally over the dam’s spillway. We don't have the legal or physical ability to hold on to that water.

When Lagunitas, Bon Tempe and Alpine are full, the overflow spills into other district reservoirs downstream. Water from Phoenix, Kent, Nicasio and Soulajule flows into local creeks where it provides many environmental benefits including habitat for endangered coho salmon and other fish and wildlife. Thus even water that goes over the spillways is put to good use.

MMWD's water rights are granted by the State of California. The rights specify how much water we can legally divert from our local creeks and store in our reservoirs. As part of these reservoir storage rights, water is also released into the creeks to provide in-stream flows for the fish.

When the district last filed for rights to expand storage in 1980, the result was 15 years of studies and hearings prior to reaching a court-ordered agreement. Since that time, stronger protections have been put in place for endangered coho salmon. Given the water needs for fish and the high volume of water we already divert, it is highly unlikely that MMWD would be granted the necessary approvals to further increase reservoir storage.

In 2014, we completed a bathymetric survey of Bon Tempe Reservoir, using sonar and laser technologies to map the bottom of the reservoir and determine its current capacity. The last study of the reservoir’s capacity was conducted when it was built in the late 1940s. The new survey found that sedimentation is not a problem in Bon Tempe. In fact, using modern methods we found the capacity of Bon Tempe is greater than the measured capacity calculated in the 1940s study. MMWD is currently performing similar studies on our other reservoirs.

It's possible that MMWD could obtain permission from the state to restore reservoir capacity lost due to sedimentation. However, removing accumulated sediment would be a challenging and expensive project. It would likely require extensive review, permitting, mitigation and likely cost in the range of $50 to $70 million.

Though we cannot increase the amount of storage, we are able to use our storage strategically to make the most of it. This can include maximizing use of Nicasio Reservoir (which fills faster than the other reservoirs when it does rain), using our reserve reservoirs Phoenix and Soulajule as needed, maximizing the use of recycled water and Russian River water to preserve our reservoir supply, and other operational adjustments.

The simplest and least expensive way we can maximize our water supply is through conservation. That's why we ask our customers to use water wisely and why we offer a variety of conservation programs and rebates to help.